Dark Water's Embrace — Stephen Leigh

A century ago a small group of humans was marooned on a distant planet. Now their descendants struggle with rising infertility, mortality and mutation, for which no cause--or cure--can be found.

Then comes a startling revelation: The preserved corpse of a member of the planet's long-extinct native race bears deformities nearly identical to those of Anais, the settlement's doctor. Anais must discover the link between the mysteries of the planet's past and the plight of the present-day humans, before she is exiled forever--thwarting her society's last chance for survival.